A. Field of the Invention
The present invention relates generally to the fields of polymer chemistry. More particularly, it provides a variety of compositions and methods for use in the formation of polymers having an increased adhesion to ice.
B. Description of Related Art
Each year numerous automobile accidents, as well as pedestrian accidents are caused by ice on the roadways or sidewalks resulting in extensive property damage, human suffering, and sometimes the loss of human life. The development of new ways to increase the adhesion of articles of manufacture such as tires or footwear to ice would likely result in fewer accidents.
There are a variety of methods used to reduce the amount of slipping and sliding of tires and other articles of manufacture on surfaces covered with ice. These methods include attaching studs or spikes on the surface of a car tire to incorporating hard powders such as silica to the surface. This can be damaging to the tire and the surface and can cause reduced traction when the surface is not icy.
There are generally three existing approaches to the problem of traction on ice: 1) materials which will enhance friction on ice, 2) devices designed to increase friction by digging into the ice; or 3) destruction of the ice itself.
1. Materials that Enhance Friction on Ice
Examples of the first approach include modifying the surface of the article. This has been accomplished by spraying a polymer or other coating material onto the surface of a tire or shoe sole. One traction composition comprising a lignin-based phenolic compound, a silicone resin, a rosin, and a suitable carrier that is sprayed onto a tire or shoe to impart anti-slip properties is discussed in U.S. Pat. No. 5,530,040.
Similarly, Insta-Trak, Prestone's wood-rosin-based spray, which was intended to be applied to automobile tires at the point of use, is claimed to increase traction on ice for a time. However, it wears off after driving a moderate distance.
Products such as “Tyre-Grip” (http://www.tiregrip.com) and “Sure-Drive” (http://www.improvementscatalog.com), “Shoe-Grip” and “Sure-Step” (http://www.shoplifestyleonline.com) are also sprayed on the tire or shoe surface from an aerosol can, and wear off after moderate use (e.g., 50 miles for Insta-Trak). These products must be repeatedly sprayed onto the surface for a continuous increased traction on ice or snowy surface.
Bridgestone has developed a tire having a foamed rubber layer (see for example U.S. Pat. No. 6,497,261, U.S. Pat. No. 6,021,831, and U.S. Pat. No. 5,788,786). This is based on the idea that ice, even below freezing, has a thin layer of liquid on its surface. The tire has a spongy surface designed to absorb this, so that the tire would contact the solid surface only.
3M produces a rough material called “SafetyWalk” which is supposed to enhance traction in general—not just on ice. It comes as adhesive-backed sheets, which can be applied to a variety of surfaces to provide traction. U.S. Pat. Nos. 6,258,201 and 6,024,824 describe methods of making polymeric articles having better traction or non-skid characteristics by heating the particles and forcefully impinging them into the polymer so that they are at least partially embedded in the polymer. The particles used may be frictional articles including quartz, aluminum oxide, carbon black, and coal slag.
2. Digging into Ice for Increased Traction
Examples of the second method, including devices designed to increase friction by digging into the ice, are much more common and include tire tread compounds containing silica, mineral silicates, or other materials (U.S. Pat. Nos. 4,427,831, 4,918,142, 5,681,874, 5,967,211, 5,929,156, 5,530,040, 5,967,211, 6,228,908, 6,378,584, 4,427,831, and U.S. Patent Apps. 2002/0037950 A1, and 2002/0026003 A1) tires with sipes (U.S. Pat. Nos. 6,250,354, 6,026,875, 6,003,595, 5,873,399, and 5,833,779), tire chains, studs, shoe cleats, and spreading sand.
Another method to increase friction includes modifying an article with a polymer that has an increased grip on an icy surface. U.S. Pat. No. 6,228,908 describes an elastomer having a diene polymer or copolymer containing carbon-tin bonds and terminal hydroxysilanes and an optional filler silica. This polymer is used to form treads on tires having good wet traction and rolling resistance on ice. Another polymer with improved steering and traction performance on snow and ice is described in U.S. Patent App. 2002/0037950 A1. This composition has paper, a rubber component, and preferably silica and short fiber. U.S. Patent App. 2002/0026003 A1 describes a rubber composition for tire tread having diene rubber, glass fibers, a reinforcing agent, and a silicone rubber powder which has improved performance on snow and icy roads. Similar compositions include a rubber for tire tread having a rubber combined with silica, a silane coupling agent, and a powdered cellulose material and are described in U.S. Pat. No. 6,378,584. A composition for a tire with several elastomers reinforced with carbon black and silica-reinforcing fillers is described in U.S. Pat. No. 5,681,874. The addition of silica reinforcing filler was found to increase traction on icy roads. Each of these compositions require the addition of silica or glass fibers for improving traction on wet or icy roads.
Yet another polymer is described in U.S. Pat. No. 4,427,831 which describes a rubber material comprised of norborene and rubber that has an ice gripping capabilities. U.S. Pat. No. 5,967,211 discloses use of certain additives for rubber, possessing hydroxyl groups (in the case of cellulose fibers) or silanol groups (in the case of ceramic microspheres) on the surface, to enhance traction on ice. The hydroxyl or silanol groups are used because of their reactions with special additives that bind rubber, cellulose and silica together. No mention is made of the spatial arrangement of said hydroxyl or silanol groups. The particles are used simply to provide a rougher surface as the tire wears down (rougher, relative to a tire without the fibers and spheres but otherwise the same composition). Similarly, U.S. Pat. No. 5,929,156 discloses the use of amorphous silica as an additive to rubber. This silica has a random structure and is not designed with particular spacing of hydroxy groups.
Numerous inventions have incorporated amorphous silica or other materials with rubber in order to create a tire that has increase adhesion or friction to ice. However, the prior art does not use silicate polymers and can not use the ordered arrangement of silicate polymer to help grip the ice surface. While there are numerous competitive products, no composition discussed above uses surface adhesion from preorganized groups of atoms to enhance adhesion to ice.
Since cleats, tire chains, etc., do not use atomic adhesion, but simply dig holes, they can effect only a minor improvement towards increasing friction. In addition, these all have their own drawbacks: cleats and the like tear up wooden floors, carpets, electrical cords, fire hoses, etc., and can be worn down by concrete. Studded tires can damage road surfaces and are banned in some states.
3. Destruction of the Ice to Increase Friction
An example of the third approach to the problem of traction on ice is to melt the ice with road salt. Salt, though cheap, is needed in enormous quantities, and is notoriously corrosive, driving up the cost of auto maintenance. The large amounts needed every year can adversely affect trees, soil bacteria, and other members of the ecosystem. Salt substitutes exist, but they all cost considerably more per ton than ordinary salt, and still possess in some degree the adverse effects of ordinary salt.
4. Other Mechanisms for Ice Adhesion
Naturally occurring molecules have been found to inhibit ice growth by adsorbing to ice and inhibit ice crystal growth. These proteins and peptides are produced by several species of fish. Haymet has studied the use of winter flounder “antifreeze” proteins that inhibit ice growth in Antarctic fish. These proteins have four threonine side chains equally spaced 11 residues apart that were mutated to other residues. It was found that when the hydroxyl moiety in the threonine residue was replaced with a hydrophobic methyl group from valine and alanine, the ice growth inhibition was not significantly changed. However, this study was focused on the mechanism of an expensive protein in inhibiting ice and does not provide a composition for increasing the traction on an icy surface.
The concept of designing specific artificial chemical agents whose purpose is to control the physics of ice is described in U.S. Pat. No. 6,303,388. This patent describes a process for preparing ice-controlling molecules that can be used to inhibit the incorporation of additional water molecules into the structure and thereby inhibit ice crystal growth, recrystallization, and sublimation. These compounds are also intended to postpone or prevent ice nucleation. The process includes the steps of (1) selecting a template that nucleates ice, (2) testing a molecule to see if it is capable of binding to the template, (3) testing the molecule to see if it inhibits ice crystal growth, and (4) identifying the molecule as an ice interface dopant. The process of this invention is primarily directed at molecules that prevent growth specifically in the direction of the c-axis. This patent provides a process of preparing molecules that will inhibit ice growth and provides several ball-and-stick diagrams with oxygen atoms each to demonstrate the invention. Exemplary classes of dopants are described by molecular structure 3 which simply gives the lattice structure of ice and depicts how atoms in branched and ring structures match the ice lattice. Particularly, U.S. Pat. No. 6,303,388 describes a heterocyclic structure having six 6-membered rings containing two oxygen and three hydroxy groups bound to the multiple ring structure. Three other structures provided in the patent are heterocyclic structures C18H21O3, C10H16O2, and C9H13O2.
It would therefore be advantageous to develop a material with ice gripping properties that is either adhesive and stable enough not to require frequent application or strong enough to be formed into an article of manufacture such as, for example, a tire tread or shoe sole.